Adding 3 point belts to 60's cars

[eltax91]

Hi guys

I'm seriously starting to get swayed by classic mustangs. A car I've (like many) always lusted after. I'm looking at 60's coupe and the odd 'vert cars in the £15k bracket, but the crucial thing is, this is to be a fun classic I could use on sunny days and those largely happen at family time.

I've got 2 kids, one is 4 and the other 4 months. They both have car seats that require a 3 point belt. I'm guessing this wasn't a concern to the designers of the 60's.

So, being a total newbie here, can anyone tell me if it's possible to safely retrofit 3 point belts in the rear?